This invention relates to a gas bag module comprising a gas bag.
Known gas bags have a front wall for the impact of the occupant and an indentation starting from the front wall, which indentation is formed in that a center portion of the gas bag wall is prevented from moving freely during inflation and is restrained, the gas bag having an annular chamber to be filled with gas and provided around the indentation. In such ring-shaped gas bags, the center portion which in a conventional gas bag is presented to the occupant, is prevented from being inflated and from moving towards the occupant in that it remains attached to the module. In this arrangement, restraint is effected via the ring-shaped front wall around the indentation. The indentation is to be as small as possible so as to help the head of the occupant to be intercepted as safe as possible.
The invention provides a gas bag module in which the indentation is closed at least in part, preferably completely. This is achieved in a gas bag module comprising a gas bag, an outer contour of the gas bag being defined by a gas bag wall which has a front wall for the impact of an occupant and an indentation starting from the front wall. The indentation is formed in that a center portion of the gas bag wall is prevented from freely moving during inflation and is restrained. The gas bag has a ring-shaped chamber to be filled with gas and extends around the indentation. Arranged in the indentation is at least one limiting strap which extends along the indentation and has an end pointing out of the indentation and, related to an inflated condition of the gas bag, is attached to the gas bag wall at least at the end pointing out of the indentation. By means of the at least one limiting strap arranged in the indentation, the indentation is preferably completely closed in the region of that end of the limiting strap which points out of the indentation. The gas bag itself preferably is a front gas bag accommodated in the steering wheel or in the dashboard, which front gas bag is inflated in the case of a frontal impact.
In accordance with the preferred embodiment, the limiting strap is attached to the gas bag wall in the region of transition from the front wall to the indentation. Thus, the limiting strap pulls the area of the gas bag wall to which it is attached preferably radially inwards, into the indentation, so that the same is reduced in its cross-section.
Moreover, it is, however, also possible to provide a short limiting strap, so that due to the gas pressure the gas bag wall bulges radially inwards behind the end of the limiting strap pointing outwards or, in other words, collapses radially inwards from all sides, so that in the fully inflated condition an outwardly closed wall is present upon which the occupant can impact.
Preferably, a plurality of limiting straps is provided, which limiting straps extend obliquely, i.e. at an angle in the indentation during inflation and exert a lateral tensile force on the gas bag wall, which causes closure of the indentation.
In this connection it should be emphasized that possibly a complete closure, so that there is no passage at all, is not possible. Therefore, minimum passages from the outside into the indentation may occur.
In the approximately fully inflated condition, i.e. in a not completely inflated condition, the limiting straps extend in a Y-shaped or X-shaped manner, so that the lateral tensile force can be applied. The angle of intersection of the limiting straps with respect to each other is changed in the course of the further inflation in so far as it is reduced up to the fully inflated condition. This means that in the fully inflated condition the limiting straps which for instance extend in an X-shaped manner with respect to each other, are disposed with respect to each other such that they form an inverse xe2x80x9cVxe2x80x9d in a side view.
In the case of a Y-shaped limiting strap it is provided for that a limiting strap from the module-side end of the indentation, before being attached to the gas bag wall, is divided into several limiting straps, e.g. in that several limiting straps are sewn to the one limiting strap. The several limiting straps preferably rest against each other or almost against each other in the completely inflated condition, when the limiting straps have pulled tight the indentation.
In accordance with the preferred embodiment, the gas bag consists of several fabric parts, one fabric part thereof forming the front wall and having a centric opening for defining the region of transition to the indentation. This opening is preferably slot-shaped, which facilitates the automatic closure of the indentation.